Various RF communication systems are known in the art, including trunked communication systems. The latter typically administer a plurality of communication resources, often using frequency division multiplexing, time division multiplexing, and/or code division multiplexing to define a particular channel that can be assigned to support communications between various communication units. Since these communication resources typically remain undedicated to a particular unit or group, they must be assigned from time to time as needed. To facilitate the assignment process, an assignment resource is often provided. For example, one or more communication resources may be utilized as dedicated assignment resources that are used by the resource controller of the system and the various communication units to communicate with one another with respect to resource allocations. (Pursuant to another approach, the assignment resource can be combined with other communication resources; for example, control data supporting the assignment process can be subaudibly combined with voice traffic occurring on the same frequency.)
Regardless of the specific assignment resource configuration, a selection of any particular configuration or architecture will necessarily limit, at some upper level, the number of communication units that can be appropriately serviced by the communication system. For example, a typical Smartnet trunked radio system can only accommodate about 21 channels, presuming that one of these channels constitutes a dedicated control resource, leaving the remaining 20 channels to support voice and other user-to-user communications. There are applications, however, when 20 voice channels will not suffice to meet anticipated needs. For example, a particular user may require 27 voice channels to meet anticipated needs.
One prior art approach to increase system loading capabilities would be to increase the baud rate for data transmissions on the assignment resource. While this will indeed allow a greater number of channels to be accommodated by the resulting system, such a system will not be compatible with communication units already in the field, since those pre-existing units will not compatibly transceive the data having the increased baud rate.
Another prior art solution would be to simply dispense with certain currently supported messages on the assignment resource, thereby providing more time for more messages pertaining to additional channels. Simply eliminating certain classes of messages, however, typically requires that various system features be dispensed with, and this often presents an unacceptable solution.
Yet another prior art approach would be to provide more space for additional channel messages by reducing the channel requirements for currently supported messages. For example, a complete resource grant message in a Smartnet system currently constitutes an original transmission of a resource allocation signal, subsequently followed by three repetitions. By eliminating some or all of these repetitions, additional space for additional messages could of course be accommodated. Unfortunately, this approach can greatly degrade the overall performance of the system. Many communication units require some or all of the repeated resource allocation grants due to the high noise environment, RF fades, and weak signal area conditions that frequently prevail in an RF environment, and particularly a landmobile radio communication system.
A need accordingly exists for a communication system that can support an increased number of communication resources, in a manner compatible with existing communication units, and in a manner that will not unduly compromise the operating integrity of the system.